ABS Woes

MarkIII4Me

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What does it mean when the abs light constantly flashes when pulling codes. Just none stop quick flashing. TSRM says nothing about it. Unless it’s a bad ECU, but that should be a solid light according to the TSRM, unless I’m reading that wrong.

Ideas?
 

MarkIII4Me

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Ok, so a flash every half a second means there are no faults. I clear them. Light is off, 10 seconds of driving light goes solid. Remove the diag connector and get constant quick flashing, which apparently means the system is working correctly. What the hell?
 

MarkIII4Me

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Tried a different ABS ECU and same thing. Light initially off, comes on within the first 20 seconds of driving. Light flashes rapidly when in diagnostic mode, signifying no faults. Now what?
 

Piratetip

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Have you swapped any parts or have a mismatch of parts / ecu / abs /wiring / harness from different year cars?

I tried swapping in a newer ABS computer to my 87, but had this exact issue.
ABS was solid on, no codes, no abs working.
I swapped back to the 87 abs computer and everything was fine again.
 

MarkIII4Me

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Car is Frankenstien'd man. Different rear ABS sensor (came with the r154), pretty sure it has a manual harness swapped from the original automatic one, both were gray plug tho. ABS ECU should be the original from 1990. The test one I installed today came out of a 89. Part numbers on it are shot tho. The one out of my car is legible. I never new there were different ECU's. Could I need an earlier unit?
 

Piratetip

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Yeah could get messy then.
Has the ABS ever worked?
 

Piratetip

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Oh I see you said the ABS light comes on after driving.
My best guess is that you have a mismatch of speeds now between the front and rear sensor.
You swapped transmissions but probably not the driven and drive gears in the r-154 to match your final drive (diff) ratio.

I bet the ECU is detecting a speed difference outside it's working range between front and rear and throwing the light.
Or the sensor/wiring is bad somewhere.
 

Piratetip

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Actually now, that was a brain fart.
The driven and drive gears are for the speedometer not the abs.
Hmm....
Have to think on this.
 

MarkIII4Me

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Before the tear down the abs worked correctly. My old rear wheel speed sensor went with the auto trans, but the r154 came with one. However the wires where cut and discolored. Originally I had the rear left and right wires flip flopped. But the correction didn’t seem to make a difference. When checking faults I had them for right front and left front wheel speed sensors and the abs pump relay. Tested relay, and to no surprise, it was good. Recently I found the two 6 plug connectors at the pump (gray and black) plugged in opposite. I thought no way it was that all along. I plugged the abs ecu back in and low and behold, no abs light on startup. Drove 100 feet and it came on solid. Checked faults and it flashes quickly as if there are none. One other thing. I did extend all of the computer wiring to run the EFI ECU under the driver seat, and I believe that extends to the abs ecu as well. Maybe I flopped two similar colored wires, but I doubt it.
 

MarkIII4Me

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I’m gonna try another ecu off a friend next week. Clearly an earlier model than the last 2 I tried as his has a single label with green writing. Doubt it’ll work, but worth a shot. 541AF58C-5DF5-44E8-B6CA-BA8AA87E150F.jpeg
 

Dave 1jz

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Before the tear down the abs worked correctly. My old rear wheel speed sensor went with the auto trans, but the r154 came with one. However the wires where cut and discolored. Originally I had the rear left and right wires flip flopped. But the correction didn’t seem to make a difference. When checking faults I had them for right front and left front wheel speed sensors and the abs pump relay. Tested relay, and to no surprise, it was good. Recently I found the two 6 plug connectors at the pump (gray and black) plugged in opposite. I thought no way it was that all along. I plugged the abs ecu back in and low and behold, no abs light on startup. Drove 100 feet and it came on solid. Checked faults and it flashes quickly as if there are none. One other thing. I did extend all of the computer wiring to run the EFI ECU under the driver seat, and I believe that extends to the abs ecu as well. Maybe I flopped two similar colored wires, but I doubt it.
You say you have changed the wires of the rear sensor? Was this at the connector between engine and sensor harness? How is this connected now color to color? Did you check the TSRM thoroughly when doing this ?
 

MarkIII4Me

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I can’t remember how I figured out the wires were swapped, but that’s going to be the first thing I check.
 

3p141592654

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A rear sensor issue should set code 33. In the case where the light comes on but no code is stored there are a couple of possibilities. The one that stands out is "the computer is not properly connected". Given the harness was extended, this seems possible and should be carefulyl checked.
 

MarkIII4Me

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Pireatip does brought up a good point. Once cleared, the abs light does not illuminate until driving the vehicle for over 100ft. Like it’s getting a discrepancy in sensor readings. So thinking I might have had or currently do have the rr+ and rr- wires swapped, which may have internally shorted the sensor, or just might need to be swapped again. It’s worth a shot. I really would like a new sensor tho if I could find one, as that would be the easiest way to rule it out.

0E74B0A9-B210-435A-96B7-7F768A4B3511.jpeg
 

Piratetip

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I would test the sensor first before just buying another.
The TSRM shows how to do this.

Yes, also check that it is wired correctly.
 

MarkIII4Me

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Test plan shows the use of an Oscilloscope. Any way around this? I wish I could just ohm the sensor out to make sure it isn’t damaged. Even if the wiring is correct, the sensor may be toast from before I swapped the +/- wires, yet still isn’t throwing a fault code.
 

Piratetip

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This check as well at the bottom.
Will give you indication that it is switching between 12v and less than 2V.
 

3p141592654

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Pireatip does brought up a good point. Once cleared, the abs light does not illuminate until driving the vehicle for over 100ft. Like it’s getting a discrepancy in sensor readings. So thinking I might have had or currently do have the rr+ and rr- wires swapped, which may have internally shorted the sensor, or just might need to be swapped again. It’s worth a shot. I really would like a new sensor tho if I could find one, as that would be the easiest way to rule it out.
I understand your point, but a bad rear sensor should set a code 33. If the light comes on and stays on then you have Problem No. 1. You can follow the flowchart here. http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=BR&P=55

If the light comes on above 6mph and goes off below 6 mph then you have Problem No. 3.
 

Dave 1jz

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Pireatip does brought up a good point. Once cleared, the abs light does not illuminate until driving the vehicle for over 100ft. Like it’s getting a discrepancy in sensor readings. So thinking I might have had or currently do have the rr+ and rr- wires swapped, which may have internally shorted the sensor, or just might need to be swapped again. It’s worth a shot. I really would like a new sensor tho if I could find one, as that would be the easiest way to rule it out.
Swapping rr+ and rr- (polarity) will not kill the sensor. Strangely the engine harness RR+ is black and goes into the sensor as white. I have made the same mistake in the past and took a long time to find out. The ABS ecu did throw a code for the rear sensor..
 

MarkIII4Me

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I remember at one point I tried to activate the abs pump by shorting connector B’s SRR, SFL, and SFR to positive. It did not work. In sheer frustration, I thought I had my connectors confused and did the same thing to Connector A and it sparked when I shorted GND, obviously. The abs ecu was not connected at the time. I’ve checked the abs fuse and it is not blown. Could I have damaged the pump and still not throw a fault?

575A749E-DED8-43B0-AC26-A97CB2CAE77F.jpeg
 

MarkIII4Me

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Swapping rr+ and rr- (polarity) will not kill the sensor. Strangely the engine harness RR+ is black and goes into the sensor as white. I have made the same mistake in the past and took a long time to find out. The ABS ecu did throw a code for the rear sensor..
Did the sensor throw a fault when you had the those wires swapped incorrectly?
 

Dave 1jz

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Are you sure the rear ABS sensor is the correct one for the R154? The part number is on the sensor, so easy to check.
 

Dave 1jz

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This might cause the issue, you could measure if the tip of the sensor is close enough to the gear. It looks like the sensor itself is not giving the issue, but it might not give any reading.
 

Dave 1jz

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I would not be so sure of that. Code 33 only shows when something is malfunctioning or broken. My point is perhaps the ABS ECU sees no speed on the rear wheels to make the calculations and then throws the light when driving.

Things to check are; by oscilloscope if a signal is coming and check if this signal is a square signal, not sure if the ABS ecu will take a wave input on the rear sensor.

Ow and the RR+ an RR- is a twisted pair, this is still the case right?
 

MarkIII4Me

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Not sure what you mean by “twisted pair”. Those 2 wires are as separate as the PSEN wire. Do you know where a standalone EMS would get the VSS from? I always thought it was the rear speed sensor. I run the AEM v1 EMS and the vehicle speed reading is very accurate on throttle. Goes pretty haywire off of throttle tho.
 

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"Twisted pair" is for signals that are balanced (two coupled equal but opposite voltages) and/or for signals that are low voltage. Twisting the two wires together helps immensely with noise pickup, keeping the low-voltage signal clean.

Making a twisted pair is as easy as putting two wires in a drill chuck, and twisting away holding the wires taut. The twist rate doesn't matter much, but it should be enough that the two wires naturally stay together. Obviously fatter wire will twist with fewer twists per inch than small wire.

I suspect the signal coming out of the speed sensor is not very large.
 

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If you simply unplug the rear sensor on a working abs system it will store a code 33 once the car is moving and it detects that there is no signal. It can't do that with the car stationary.

If the R+ and R- are true differential signals then it won't matter if they are swapped. The phase of the rear signal is arbitrary anyway.

Again, since the ABS ECU was extended, I would recommend you trace every wire in the harness to make sure something didn't get mixed up. Your error flow indicates bad wiring is likely.
 

Dave 1jz

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If you simply unplug the rear sensor on a working abs system it will store a code 33 once the car is moving and it detects that there is no signal. It can't do that with the car stationary.

If the R+ and R- are true differential signals then it won't matter if they are swapped. The phase of the rear signal is arbitrary anyway.

Again, since the ABS ECU was extended, I would recommend you trace every wire in the harness to make sure something didn't get mixed up. Your error flow indicates bad wiring is likely.
NOT TRUE!!!! The polarity must be correct, otherwise you will get code 33.
 

Dave 1jz

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Not sure what you mean by “twisted pair”. Those 2 wires are as separate as the PSEN wire. Do you know where a standalone EMS would get the VSS from? I always thought it was the rear speed sensor. I run the AEM v1 EMS and the vehicle speed reading is very accurate on throttle. Goes pretty haywire off of throttle tho.
Normally the speed signal comes from the reluctant speed sensor mounted behind the speedometer, driven by the mechanical cable. This is the pink wire going to the stock ecu. The ABS is a separate system, and i am not sure how this system will act up when you piggyback speed ref signals.
 

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Just to add my 2 cents. I've piggybacked off the ABS sensors for speed sensors for my MS3 pro and didn't have a problem. I grab both front and rear for vss 1 and 2 as the pink wire causes jumpy results due to the stiff drive cable. (speed sensors used for traction control)
 

MarkIII4Me

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Not sure if this helps any, but right before the ABS light illuminates, (usually within the first 10 seconds of moving), I can hear loud solenoid noise from the engine bay which must be the ABS pump activating, then the ABS light illuminates. When shutting off power, the light goes out until the process is repeated. Pulling codes causes ABS light to flash rapidly as there are no codes present.
 

MarkIII4Me

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Exactly. The ecu seems to be working, as when I unplug the black 4 pin connector to the pump, it instantly flashes a code 11 for open circuit.
 

Piratetip

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Interesting. Yeah .5 second continuous flashes indicate no codes.
But it's clearly triggering the light while driving for some reason.
Could be your issue is outside of the 15 different available codes.
Or it does not know how to classify the fault.

My guess is it has to do with a mismatch in speed front and rear between the sensors.
But you are probably going to have to manually verify all 3 wheel speed signals are making it to the ECU.
Backprobe the connectors and start manually diagnosing your issue.
Could be another issue with wiring as well.
It's going to probably take some meticulous tracing of wiring and matching signal inputs / outputs to what they should be.

I'd start with the TEWD ABS section.